DIRECT BGA SOCKET FOR HIGH SPEED USE

• US 20020076966A1
• Filed: 12/20/2000
• Published: 06/20/2002
• Est. Priority Date: 12/20/2000
• Status: Active Grant

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Carron, Ted, Gattrell, David C., Jakola, Eric J., Morrison, Richard C.
• Granted Patent: US 6,416,332 B1
• Time in Patent Office: Days
• US Class Current: 439/330
• CPC Class Codes: H01R 13/2421 using coil springs
• CPC Class Codes: H01R 4/024 comprising preapplied solder

Abstract

The present invention relates to a socket for testing ICs and, in particular, high speed ICs in BGA packages. The socket uses resilient conductive test pads positioned on a substrate in an array to match an array of spherical contacts of the bottom of a BGA package. The BGA package is aligned with the test pads by the use of holes centered on the test pads into which the spherical contacts are seated. The holes may also be used to interconnect conductive signal paths on layers of the substrate.

The present invention is also directed to a means of holding an IC package in position in the test socket. In particular, the test socket is provided with two flexible seals on the top of a support, which encircle the test pads. The flexible seals, together with a top surface of a support and a socket lid define an enclosed cavity. A vacuum is applied to the enclosed cavity, which compresses the flexible seals and pulls the socket lid towards the test pads. The bottom surface of the socket lid is adapted to apply downward force to the IC package to force the IC package leads into contact with the test pads when the socket lid is moved towards the test pads.

Claims

1. A socket for an integrated circuit package having spherical contacts on its bottom surface, the socket comprising:

a nonconductive substrate;

a plurality of conductive circuit paths on the substrate;

an array of resilient electrically conductive pads on the substrate having substantially the same configuration and pitch as the spherical contacts on the package;

the array of electrically conductive pads being selectively electrically connected to the conductive circuit paths;

a means of aligning the spherical contacts with the conductive pads; and

a means for bringing the spherical contacts into electrical contact with the electrically conductive pads;

wherein when the electrically conductive pads electrically contact the spherical contacts, and the resilience of the electrically conductive pads compensates for any lack of planarity in the spherical contacts.

2. The socket of claim 1 wherein the means of aligning the spherical contacts with the conductive pads is a hole extending through each of the electrically conductive pads and wherein the holes are smaller in diameter than the electrical contacts and are adapted to receive a lower portion of the spherical contacts.

3. The socket of claim 2 wherein the holes are substantially centered on the electrically conductive pads.

4. The socket of claim 2 wherein the holes extend through the substrate.

5. The socket of claim 4 wherein the holes are electrically plated.

6. The socket of claim 2 wherein a diameter of the holes is at least ⅓

and no more than ½

the diameter of the spherical contacts.

7. The socket of claim 1 wherein the means of aligning the spherical contacts with the conductive pads is a support surrounding the conductive pads defining an opening substantially the same size as the package such that when the package is positioned in the opening the spherical contacts are aligned with the conductive pads.

8. The socket of claim 5 wherein the substrate is a multi-layer printed circuit board and at least one of the holes connects to a circuit path on an internal layer of the printed circuit board.

9. The socket of claim 4 wherein a first plurality of the holes are connected to high frequency conductive circuit paths and are not plated and a second plurality of the holes are connected to low frequency conductive circuit paths and are plated.

10. The socket of claim 1 wherein the conductive pads are comprised of a conductive elastomer.

11. The socket of claim 10 wherein the elastomer is in the range of 0.25 to 0.50 millimeters thick.

12. The socket of claim 1 wherein the conductive pads are comprised of a polycarbonate.

13. The socket of claim 1 wherein the conductive pads are comprised of a thermoplastic compound.

14. The socket of claim 1 wherein the socket is a test socket for testing the functionality of the integrated circuit within the package.

15. The socket of claim 1 wherein the means for bringing the spherical contacts into electrical contact with the electrically conductive pads comprises;

a support on the nonconductive substrate defining an opening for the integrated circuit package;

a removable lid having a substantially flat bottom surface;

a first flexible seal on the support surface surrounding the opening;

a second flexible seal outside the first flexible seal on the support surface surrounding the opening;

the support surface, the bottom surface of the lid, the first flexible seal and the second flexible seal defining a cavity; and

a means of applying a vacuum to the cavity;

wherein the vacuum compresses the first flexible seal and the second flexible seal thereby forcing the lid to apply a downward force to the package to bring the spherical contacts into electrical contact with the electrically conductive pads.

16. The socket of claim 15 wherein the support has at least two guide pins adapted to mate with the lid and guide it into position.

17. The socket of claim 15 further comprising a spring means attached to the bottom surface of the lid and wherein the vacuum compresses the spring means which then applies a downward force to the package.

18. The socket of claim 1 further comprising a plurality of non-compliant electrically conductive pads underlying the resilient electrically conductive pads.

20. The apparatus of claim 18 wherein the means of applying a vacuum to the cavity comprises a hole extending through the support having a first end inside the cavity and a second end outside the cavity and a vacuum supply connected to the second end.

21. The apparatus of claim 18 wherein the top surface of the support has at least two guide pins adapted to mate with the lid and guide it into position.

23. The socket of claim 21 wherein an upper edge of a plurality of the array of holes is conductively plated and the means of electrically connecting the conductive circuit paths to the spherical contacts comprises;

a support on the nonconductive substrate defining an opening for the integrated circuit package;

a removable lid;

a first flexible seal on the support surface surrounding the opening;

a second flexible seal outside the first flexible seal on the support surface surrounding the opening;

the support surface, the bottom surface of the lid, the first flexible seal and the second flexible seal defining a cavity; and

a means of applying a vacuum to the cavity;

wherein the vacuum compresses the first flexible seal and the second flexible seal thereby forcing the lid to apply a downward force to the package to bring the spherical contacts into electrical contact with the conductively plated upper edge of the plurality of the array of holes.

24. The socket of claim 21 wherein the nonconductive substrate is comprised of a flexible material with a compressible backing and a solid support.

19. An apparatus for retaining a plurality of contacts of an integrated circuit package in contact with a plurality of pads of a socket comprising:

a support surrounding the pads and defining a socket opening for the integrated circuit package;

a removable lid having a substantially flat bottom surface and a spring means attached to the bottom surface;

a first flexible seal on a top surface of the support surrounding the opening;

a second flexible seal outside the first flexible seal on the top surface of the support surrounding the opening;

the top surface of the support, the bottom surface of the lid, the first flexible seal and the second flexible seal defining a cavity;

a means of applying a vacuum to the cavity;

wherein the vacuum compresses the first flexible seal and the second flexible seal thereby forcing the spring means on the lid to apply a downward force to the package to bring the spherical contacts into electrical contact with the pads.

22. A socket for an integrated circuit package having spherical contacts on its bottom surface, the socket comprising:

a nonconductive substrate;

a plurality of conductive circuit paths on the substrate;

a means of selectively electrically connecting the conductive circuit paths to the spherical contacts; and

an array of holes on the substrate having substantially the same configuration and pitch as the spherical contacts on the package, each of the holes in the array of holes having a diameter which is at least ⅓

but no more than ½

of a diameter of the spherical contacts;

wherein the holes are adapted to seat the spherical contacts.

25. The socket of claim 23 wherein the lid further comprises a spring means attached to a bottom surface wherein the spring means applies the to force to the package.